1. Field of the Invention
The present invention relates generally to a portable terminal and, more particularly, to a vibration module for a portable terminal, which can provide a haptic feedback function.
2. Description of the Related Art
Haptic feedback refers to a method for expressing information based on a user's sense of touch and skin contact, includes providing additional meaning by a force feedback function, for example to remotely control a robot arm. Recently, efforts have been made to utilize haptic feedback in portable terminals, such as cellular phones, not only as a simple vibration function for a incoming call notification, but also as a function for providing notification that a signal value of a key selected by the user is normally input when the user manipulates a touch screen.
In general, when there is a call request, i.e. an incoming call, or when a text message is received, a portable terminal provides a vibration mode as one of various methods to provide notification of same. Operation in the vibration mode involves operating a vibration motor of the portable terminal.
Considering the portability of portable terminals, a coin type vibration motor or a cylinder or bar type vibration motor may be employed as a vibration motor in a portable terminal. However, such motors merely provide an incoming call notification function.
Recently, with the appearance of touch screen phones, which can provide a full-browsing screen when using the Internet or the like, input devices, such as keypads, are implemented as virtual keypads on touch screens. Such virtual keypads sense points contacted by a user to input signal values allocated to the points, respectively. A typical button-type keypad can provide a click feeling to a user with dome switches or the like, so that the user can recognize the manipulation of a keypad via sense of touch. Therefore, a user skilled with portable terminal keypad data entry can recognize whether figures and characters intended to be input by key manipulation are indeed being input without having to visually confirm that the figures and characters being entered by manipulation appear on a display of the portable terminal. However, when manipulating a keypad implemented on a touch screen, the user must directly confirm the input values through a display device since a click feeling cannot be provided like that provided by a button type keypad with dome switches.
As a result, efforts are being made to provide a haptic feedback function to portable terminals equipped with a touch screen type input device to enhance convenience and allow a user to avoid having to confirm input values by viewing a display device. Such a haptic function for a portable terminal is implemented by operating a vibration motor when a touch screen is manipulated.
However, conventional coin type, cylinder type and bar type vibration motors are limited in implementing the haptic feedback function due to lengthy response time thereof. That is, since a residual vibration time interval of a coin type motor, a cylinder, or a bar type vibration motor is long, a difficulty arises when recognizing via sense of touch whether signal values of keys manipulated by the user are correctly input, particularly when a user rapidly and continuously inputs various keys. A time interval of a vibration motor is a complete operation cycle, which includes a time during which operation of the motor continues due to inertia, until the motor completely stops.
Linear motors with low power consumption and high reliability have been proposed as vibration motors, with improved short response time. However, such conventional linear motors have disadvantages of having a single resonance frequency and abruptly reduced vibration power, even if an operating frequency deviates only about 2 to 3 Hz from the resonance frequency. Such conventional linear motors can sufficiently provide an alarm function, such as an incoming call notification, when operated within its resonance frequency. However, such conventional linear motors are also limited in providing the haptic feedback function since due to low response velocity. That is, the linear motor can provide sufficient vibration power after about 30 ms from the time point that an input signal is applied, and the vibration caused by inertia can be completely terminated after about 50 ms from the instant the input signal is interrupted.
Therefore, although the incoming call notification function can be sufficiently conducted using existing linear motors, there is a limit in providing the haptic feedback function for confirming accurate manipulation of a touch screen.